Hail...

Imagine a baseball dropped from an airplane flying at 30,000 feet ... imagine that baseball reaching speeds of 120 MPH as it falls to the ground ... and imagine you're under it!

Photo from
National Center for Atmospheric Research

Imagine you're driving along at 70 MPH...or your crops are under the hail producing thunderstorm...or your home is under the thunderstorm...

Hail causes $1 billion dollars in damage to crops and property each year

Credit: NOAA Photo Library, NOAA Central Library

According to NOAA, the Kansas City hail storm on April 10, 2001 was the costliest hail storm in the U.S. which caused damages of an estimated $2 billion.

Even small hail can cause significant damage to young and tender plants

Credit: NOAA Photo Library, NOAA Central Library

How does hail form?

Inside of a thunderstorm are strong updrafts of warm air and downdrafts of cold air.

If a water droplet is picked up by the updrafts...it can be carried well above the freezing level. With temperatures below 32F...our water droplet freezes.

As the frozen droplet begins to fall...carried by cold downdrafts...it may thaw as it moves into warmer air toward the bottom of the thunderstorm

But...our little half-frozen droplet may also get picked up again by another updraft...carrying it back into very cold air and re-freezing it. With each trip above and below the freezing level our frozen droplet adds another layer of ice.

Finally...our frozen water droplet...with many layers of ice - much like the rings in a tree...falls to the ground - as hail!

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How large can hail get?

Fortunately...most hail is small - usually less than 2 inches in diameter.

The largest hailstone (nearly the size of a volleyball!) fell on July 23, 2010 in Vivian, South Dakota and had a diameter of 8.0 inches, a circumference of 18.62 inches, and weighed just under 2 lbs (1 lb and 15 ounces). This was after the resident that found the hailstone put it in the freezer but had a 6 hour power outage and some melting likely occurred.

Credit: NOAA Photo Library, NOAA Central Library

Hailstones can begin to melt and then re-freeze together - forming large and very irregularly shaped hail

Is there a way to estimate hail size...or do I have to go outside and measure it?

It's often difficult to get an accurate measurement of hail diameter - especially when it's falling

The table to the right helps observers estimate the size of hail based on average diameters of common items

When in doubt - play it safe and wait until the thunderstorm has moved away before going outside to measure the size of hail

Should I be concerned about tornadoes when hail is observed?
The presence of large hail indicates very strong updrafts and downdrafts within the thunderstorm. These are also possible indicators of tornadic activity.

Often large hail is observed immediately north of a tornado track - but the presence of hail doesn't always mean a tornado and the absence of hail doesn't always mean there isn't a risk of tornadoes.

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Is there a way to simply look at a
thunderstorm and tell if it will produce hail at the ground?

There is no positive way to look at a thunderstorm in the distance and tell if it will produce hail reaching the ground.

Meteorologists use weather radar to "look" inside a thunderstorm. Since hail reflects more energy back to the radar than raindrops it often shows up in red shades.

The WSR-88D Doppler Radar can also estimate size of the hail based on the amount of energy reflected back.

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The National Weather Service considers a thunderstorm severe only if it produces ......

Damaging Wind
Gusts
58 miles per hour (50 knots) or higher

Or

Large Hail
1 inch in diameter
or larger

Or

Tornadoes

A SEVERE THUNDERSTORM WATCH means conditions are favorable for thunderstorms to become severe...or severe thunderstorms to move into the watch area. Watches are intended to heighten public awareness of the possible severe weather threat. Keep an eye on the sky and stay tuned to NOAA Weather Radio or local radio, television, or cable to know when severe weather warnings are issued for your area.

A SEVERE THUNDERSTORM WARNING means a severe thunderstorms poses an imminent danger to life and property to those in the path of the storm. When severe weather is indicated by weather radar, or is reported by trained SKYWARN Severe Weather Spotters or law enforcement officials a warning is issued immediately.

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Severe Thunderstorm warnings are sent to local radio and television stations and are broadcast over your local NOAA Weather Radio serving the warning area. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities to the danger.

Contact us if you'd like a free copy of Thunderstorms, Tornadoes, Lightning ... Nature's Most Violent Storms - a preparedness brochure produced by the National Weather Service, Federal Emergency Management Agency, and the American Red Cross.